<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box {
            width: 100px;
            height: 30px;
            margin: auto;
            box-shadow: 0 0 2px 1px #2270ff inset;
            position: relative;
            /* border: 1px solid #2270ff; */
        }

        .box:before {
            content: '';
            border-bottom: 24px solid red;
            border-right: 24px solid transparent;
            width: 0;
            height: 0;
            position: absolute;
            left: -12px;
            top: -17px;
            background-color: lightblue;
            background-color: #fff;
            transform: rotate(-45deg);
            /* box-shadow: 1px 1px 1px 0px #2270ff, 0px 0px 0px 0px #2270ff; */
            z-index: 3;
        }
    </style>
</head>
<body>
    <div class="box"></div>
</body>
</html>